简述数控机床滚珠丝杠副的特点。

阅读理解，判断正（T）误（F）。

     People use money to buy food,books, bicycles and hundreds of other things they need. When they

work, they usually get paid in money.

     Most of the money used today is made of metal (金属) or paper.But in ancient (古代的) time, people

often used all kinds of things as money. One of the first kinds of money was shells (贝壳).

     In China, cloth and knives were used as money. Elephant tusks (象牙), monkey tails and salt were

used in some parts of Africa. Rice was also a kind of money used by the ancient people in some islands.

Cows and other animals were used as money, too.

     The first copper coins( 铜币) were made in China. They were round and had a square (方形) hole

in the center.Different countries had used different metal for their money. Later some countries began to

make coins of gold and silver. But gold and silver were heavy to carry when people need a lot of coins to

buy something expensive. The Chinese were the first to use paper money. The first paper money looked

more like a note from one paper to another than the paper money used today.

( )1.People used all kinds of things as money in ancient times.

( )2.African people used copper coin as money in the old days.

( )3.People gave up gold and silver coins because they were easy to slip off.

( )4.The Indians were the first to use paper money.

( )5.The passage is mainly about the history of money.

下列选项中对制定风险管理目标时要考虑的因素描述不正确的是( )。

A．目标的盈利性

B．目标的明确性

C．目标的层次性

D．目标的定量化

钩体病的诊断依据。

对待犯罪的同志，是“惩前毖后，抬病救人”的方针。

下列关于日食的表述不正确的是（）。

A.一次完整的日全食过程的顺序是：初亏、食既、食甚、生光、复圆

B.中国的《尚书》上有世界上最早的日食记录

C.日食主要有日全食、日偏食和日环食

D.日全食是因为地球挡住了太阳光线